124 STUDIES IN IMMUNITY. 



the engulfing that takes place in the first few hours is only partial. 

 As in the previous experiment streptococci are found within appar- 

 ently vigorous cells, but since the number of streptococci injected 

 is too great, many of them remain free and develop. In these 

 doses there is not so much difference as regards phagocytes between. 

 a rabbit treated by serum and a normal rabbit. The streptococci 

 increase without any notable retarding effect on their development. 

 Eight or ten hours after injection the organisms in the vaccinated 

 animals are surrounded by an areola and are growing in the midst 

 of leucocytes while the control is nearing death. The animal re- 

 covers, however, although the bacteria are always extremely numer- 

 ous and phagocytosis is either insignificant or absent. 



The appearance of the exudate changes, however. It becomes 

 thicker and thicker and more concentrated until it is almost white 

 and its proportion of leucocytes great. This condition lasts for a 

 longer or shorter period. When the thickened exudate comes to re- 

 semble a homogeneous white pus, say 20 hours after injection, phago- 

 cytosis suddenly appears. Within a few hours later, 3 or 4 at the 

 most, all the streptococci that were swarming outside the cells are cap- 

 lured by the phagocytes. A great majority of the cells contain cocci 

 and often in numbers. This complete engulfing is followed by 

 either a final or a temporary cure; if the number of bacteria was too 

 great a relapse may occur 2 or 3 days later although the phago- 

 cytosis seemed complete. 



This delayed phagocytosis may be only partial if the culture has 

 developed too extensively. Under such conditions the animal 

 simply lives longer than the controls. Complete phagocytosis is the 

 essential condition for a cure. 



Conditions necessary for the occurrence of a delayed phagocytosis: 



Delayed phagocytosis may occur in animals that have received 

 sufficient serum whether subcutaneously or intraperitoneally. It 

 is most conveniently studied in a rabbit prepared by an injection 

 of bouillon and thereby rendered more resistant to peritoneal in- 

 fection. Under these conditions it may occur even with an amount 



in a mixture of serum and normal rabbit leucocytes without the preventive serum. 

 We have obtained different results under such conditions. We found at the 

 beginning a certain degree of phagocytosis whether the preventive serum was 

 added or not. Subsequent development took place in both mixtures. 



